Question

Three charges +q,-q,-q are placed at the corner of equilateral triangle of side 'a'. The resultant force on a charge+q placed at the centre of the triangle is

Answer 1

To find net force, you have to place a charge at the centroid of triangle.

Let us assume +q charge is there at centroid.

Also, let side of triangle be l. Then, distance of each charge to centroid = l/sqrt(3)

Force due to each charge q,F = 3kq^2/l^2.

Now, forces due to +q charge are at angle of 60 to each other. Thus, parallelogram law of vector addition, net force due +q charges will be = sqrt(3)F

Now, this force and force due -q charge are in same direction. hence, total force = (sqrt(3)+1)F = 8.2kq^2/l^2 towards -q charge.

If charge at centroid is -q, then direction of force will be opposite.